Appropriation categories are categories of government funding that group funds into areas of interest. The main appropriation categories and their number designation are listed below: 
- Research, Development, Test and Evaluation (RDT&E) appropriations fund the efforts performed by contractors and government activities required for the Research and Development (R&D) of equipment, material, computer application software, and its Test and Evaluation (T&E) to include Initial Operational Test and Evaluation (IOT&E) and Live Fire Test and Evaluation (LFT&E). RDT&E also funds the operation of dedicated R&D installations activities for the conduct of R&D programs. Available two (2) Years.
- Procurement appropriations fund those acquisition programs that have been approved for production (to include Low Rate Initial Production (LRIP) of acquisition objective quantities), and all costs integral and necessary to deliver a useful end item intended for operational use or inventory upon delivery. Available three (3) Years.
- Operation and Maintenance (O&M) appropriations fund expenses such as civilian salaries, travel, minor construction projects, operating military forces, training and education, depot maintenance, stock funds, and base operations support. Available one (1) Year.
- Military Personnel (MILPERS) appropriations fund costs of salaries and other compensation for active and retired military personnel and reserve forces based on end strength. Available one (1) Year.
- Military Construction (MILCON) appropriations fund major projects such as bases, schools, missile storage facilities, maintenance facilities, medical/dental clinics, libraries, and military family housing. Available five (5) Years.
|Appropriations Accounts||Navy||Army||Marines||Air Force||DoD Wide|
|Research and Development (R&D)||3019||2040||3600||0400|
|Operations and Maintenance (O&M)||1804||2020||1106||3400||0100|
|Military Construction (MILCON)||1205||2050||3300||0500|
Main Acquisition Category Guide
DoD 7000.14-R Volume 2A "Financial Management Regulation (FMR)": provides general guidance on the formulation and submission of the budget requests to the Office of the Secretary of Defense (OSD). It's used for a budget review, submission, presentation and justification to Congress. The guidance for appropriation categories is found in Volume 2A, Chapter 1. The definition from the guidance pertaining to Appropriations is below.
Appropriations: A provision of legal authority by an act of the Congress that permits Federal agencies to incur obligations and to make payments out of the Treasury for specified purposes. An appropriation usually follows enactment of authorizing legislation. An appropriation act is the most common means of providing budget authority. Appropriations do not represent cash actually set aside in the Treasury for purposes specified in the appropriation act; they represent limitations of amounts which agencies may obligate during the time period specified in the respective appropriation acts. 
- See Authorizations & Appropriations
AcqLinks and References:
-  DoD 7000.14-R Volume 2A "Financial Management Regulation"
-  Website: ACQuipedia "Appropriation Funds to Support Contracts"
- Website: OSD Comptroller DoD 7000.14R